Apparatus for detecting density of fluids



April 16, 1968 H. w. COLE, JR 3,377,840

APPARATUS FOR DETECTING DENSITY OF FLUIDS Filed April 22, 1966 I 3Sheets-Sheet 1 W w v WWW ATTORNEY8 April 6, 1968 H. w. COLE, JR3,377,840

APPARATUS FOR DETECTING DENSITY OF FLUIDS Filed April 22, 1966 5Sheets-Sheet 2 FIG. 6.

Q i a 868 866 648 856 FIG. 7. 8 H

8 INVENTOR. \M m \M M mm AT TORNE Y5 April 16, 1968 H. w. COLE, JR

APPARATUS FOR DETECTING DENSITY OF FLUIDS 3 Sheets-Sheet Filed April 22,1966 INVENTOR;

AT TORNEYJ United States Patent O 3,377,840 APPARATUS FOR DETECTINGDENSITY F FLUIDS Howard W. Cole, Jr., 12 Vale Drive, Mountain Lakes, NJ.07046 Continuation-impart of application Ser. No. 81,824,

Jan. 10, 1961. This application Apr. 22, 1966, Ser. No. 544,517 a Y 14Claims. (CI. 73-32)- ABSTRACT or THE DISCLOSURE,

Objects and brief description of the invention This application is acontinuation-in-part of application Serial No. 81,824, filed I an. 10,1961, now Patent Number 3,248,942; and that application was acontinuation in part of the application that issued as Patent 2,974,525,dated Mar. 14, 1961.

One object of this invention is to provide apparatus for preciselymeasuring specific gravity of fluids and other materials. The novelspecific-gravity-measuring apparatus to be described herein is usefulper se; and also may, with unique advantages, act as thedensity-compensating component of flow measuring systems.

It will be understood herein that the term fluid is intended to be broadenough to include liquids, gases, material which is partly liquid andpartly gaseous, material which is flowable although including smallsolid or semi-solid particles, or various combinations of the same.

There are described herein several embodiments of apparatus formeasuring the specific gravity or density of fluids or other material. Afeature of certain of these embodiments is that they do not depend uponthe force of gravity, and their accuracy is not afiected by anyvariations in the value of gravitational force or other acceleratingforces to which the apparatus may be subjected. This feature isparticularly advantageous when the apparatus is being used in aircraft,which may subject it to strong accelerations during the measurments,without affecting its performance. Certain embodiments of the specificgravity or density measuring apparatus include the use of a hollow body,for example a tube, or a tube having hollow balls on its ends, forcontaining the material to be tested.

The hollow body is mounted for variable positioning, or in someembodiments oscillation, about a transverse axis. An important featureis that the body is balanced about this axis so that the pull of gravityor the force of accelerations of the entire mechanism in any directionwill not aflect the position or movement of the hollow body with respectto the axis. In one arrangement, the hollow body is caused to oscillateabout this axis, with the aid of an intermittent driving force and arestoring force, and the frequence of oscillation will depend upon andbe an indication of the specific gravity of the material in the hollowbody.

Further objects, features, advantages and embodiments of the inventionwill appear from the more detailed descript ion set forth by way ofillustration, which will now be given in conjunction with theaccompanying drawings.

Brief description of the drawings 7 FIGURE 1 is a sectional view ofapparatus made in accordance with this invention for determining densityof afiuid; v

FIGURE 2 is a v sectional view of the apparatus shown in FIGURE 1, alongthe broken sectional plane 22; FIGURE 3 is a fragmentarysectional viewof a modified form of the apparatus shown in FIGURES 1 and 2;

FIGURE 4 is a diagrammatic view showing a combination for controllingthe apparatus of FIGURE 3 and for deriving an output voltage from it;

FIGURE 5 is a wiring diagram for the apparatus shown in FIGURES 1 and 2;v.

FIGURE 6 is a diagrammatic view of still another form of apparatus formeasuring density or specific gravity, also depending upon centrifugalforce; I

FIGURE 7 is a sectional view through another modified construction ofapparatus for determining specific gravity. FIGURE 8 is a sectional viewtaken on the line 88 of FIGURE 7;

FIGURES 9 and 10 are sectional views taken on the lines 99 and 1010,respectively, of FIGURE 8 and FIGURE 11 is a wiring diagram for theapparatu shown in FIGURES 7-10.

Detailed description of the invention One feature of the density orspecific gravity measuring apparatus to be described at this point isthat it does not depend upon the force of gravity, and its accuracy isnot afiected by any variations in the value of gravitational force orother accelerating forces to which the apparatus may be subjected.

The apparatus includes a hollow member, which may for example, beelongated and of tubular shape, for containing the fluid to be tested.The hollow member is supported and journaled for oscillation about anaxis passing transversely through the middle of the hollow member. Thehollow member is in dynamic and static balance about this axis. Thisarrangement is of considerable advantage in giving the apparatus thedesirable property of being unaffected by the force of gravity orvariations in accelerating forces to which the apparatus may besubjected.

Another feature of one embodiment is that, in addition to the firsthollow member which carries the fluid of unknown specific gravity, thereis provided another,-exactly similar hollow member, for carrying a fluidof known specific gravity. For each hollow member there are means, forexample, a spring, providing a force for urging it to return to itsequilibrium position when it is deflected about its axis of oscillation,and means, for example, a solenoid, for intermittently applying adeflecting force to it, to cause it to oscillate about that axis. Thetwo hollow members are supported in a common frame. Each hollow memberand its assembly for deflecting, restoring and supporting it isidentical in construction to the other. Each of the hollow members willoscillate at a frequency determined by the specific gravity of itsfluid.

By the use of electrical pickup means, there are generated twoelectrical signals corresponding in frequency respectively to thefrequencies of oscillation of the two hollow members. These twoelectrical signals are beat against one another, to derive a signal thefrequency of which is related to the difference in frequency ofoscillation of the two hollow members. Indicating means are provided forindicating a value proportional to this difference frequency, which inturn is related to the specific gravity of the fluid being measured.

In FIGURE 1, there is shown schematically a specific gravity Sensingunit 502, including a first hollow member or tube assembly 504, forcontaining the fluid to be measured, and a second hollow member or tubeassembly 506, for containing a fluid the specific gravity of which isknown. Fluid is supplied to the tube assembly 504 through a conduit 508.FIGURES 2 and 5 are returned from the tube assembly through a conduit510. It will be understood that when fluid flows through the assembly564 in parallel with supply pipe, it is necessary to provide sufficientpressure drop between the point where the conduit 508 meets the supplypipe and the point where the conduit 510 meets the supply pipe, toassure that the fluid in the tube assembly 504 is a representativesample of the fluid passing through the supply pipe.

The tube assembly 504 is shown toward the bottom of FIGURE 1 and also inFIGURE 2, and the tube assembly of 506 is shown toward the top of FIGURE1.

There is provided a lower base 512, and upper base 514, and a circularhousing 516, screwed together, and provided with rubber O-rings 518, forsealing purposes.

It may be observed generally that the assembly associated with the tubeassembly 504, in the lower half of FIGURE 1 is identical with theassembly associated with the tube assembly 506 in the upper halfthereof. The two assemblies are mounted so that the tube assembly 506runs perpendicular to the major plane in which the tube assembly 504lies, this being the plane of the paper in FIGURE 1.

There are provided a pair of mounting rails 520 and 522. These railscarry coil mounting plates 524 and 526 which in turn carry coils 528 and530, held in place by lock nuts 532 and 534. The coils are provided withcores of ferro magnetic material, 536 and 538. The coil 530 terminatesin leads 540 and 542. The coil 528 terminates in leads 544 and 546. Thevarious electrical leads are brought in through a connector 548.

The tube assembly 504 comprises an inner feed tube 550, an outermeasuring tube 552, a supply and torsion tube 554 communicating with theinner feed tube and discharge and torsion tube 556, which communicateswith the measuring tube. There is provided a hub 558 which servesseveral purposes. It aids in supporting the feed tube 550 and themeasuring tube 552 with respect to each other and with respect to thetorsion tubes 554 and 556. It is shaped to include a duct 560, providingcommunication between the interior of the measuring tube 552 and thedischarge torsion tube 556. Carried by the rails 520 and 522 are a pairof wire springs 562 and 564. In the upper half of FIGURE 1 a similararrangement is shown, and because of the orientation, may be seenclearer. The springs for the upper part of FIGURE 1 are 566 and 568. Thehub 558 has portions which include bores for receiving the springs 562and 564.

The tube assembly 504 in FIGURE 1 may be seen to be mounted foroscillation in the plane of the paper, and the springs 562 and 564 serveto provide a restoring force when they are bent by the hub 558, whichoccurs when the tube assembly is deflected about its axis of oscillationestablished by the torsion tubes 554 and 556. S01- dered to themeasuring tube 552, toward its lefthand end, in a position to cooperatewith the coil 530, is an armature 570.

A similar armature 572 is carried by the righthand end of the tube 552,in a position to cooperate with the coil 528. The coil 528 is a drivingcoil, which serves intermittently to attract the armature 572 and henceto transmit a driving force to the tube assembly 504, for producingoscillatory motion of it. The coil 530 is a pickup coil, and in responseto motion of the armature 570 by the measuring tube 552, there areproduced variations in the reluctance of the magnetic circuit for thiscoil.

One or more counterweights, for example, solder, are applied to eachoscillating tube assembly, of suflicient magnitude and at proper pointsto balance the assembly .4 about its axis of oscillation. Such acounterweight is shown in FIGURE 1 at 573. The balance should besufiiciently good to assure that, under conditions of acceleration towhich the apparatus will be subjected including linear accelerations,vibrations, and other accelerations, the output signal from the pickupcoil will not be aifected enough to give a significantly erroneousindication. For this purpose it is usually sufficient to provide staticbalance. In addition, it is desirable to provide dynamic balance. Suchconditions of balance are attained by the application of counterweights,such as the solder.

Aside from the use of counterweights to provide balance, they are alsoused to tune the tube assemblies, that is to adjust each one to adesired natural resonant frequency, and to give the two assemblies, 504and 506, identical characteristics in this respect. As shown in FIG- URE5, the coil 53% is energized from a source 574 of positiveunidirectional potential, through a resistor 576, and a resistor 578,connected to ground. At a point 580 at the upper end of the resistor 578there will appear a unidirectional component of potential, because ofbiasing affect of thecurrent from the source 574. In addition, becauseof the variations in the reluctance of the magnetic circuit of the coil536, and the consequent variations in the inductance of this coil, therewill appear at the point 580 an alternating component of potentialhaving a repetition frequency the same as the frequency of oscillationof the tube assembly 504.

The driving coil 528 is connected in the anode circuit of a vacuum tube582, which is energized from a source 584 of unidirectional voltage. Thetube 582 includes an anode 586, a control grid 588 and a cathode 590,the cathode being connected to ground. The grid 588 is biased to thecathode potential by a resistor 592, and is connected via a couplingcondenser 594 to the point 580. It

may be seen that the amplifier tube 532, the oscillating tube assembly5&4 and the connections thereto comprise an electro-mechanicaloscilaltor. That is, variations in the anode current of the tube 532will produce variations in the position of the tube assembly 504,because of the solenoid action of the coil 528, and oscillatory motionof the tube assembly 504 will produce variations in the current throughthe pickup coil 53%, and consequently variations in the voltage appliedto the grid 588 of the tube 582.

Such a system has a natural resonant frequency which depends upon anumber of factors. One of the factors upon which it depends is therestoring force supplied by the stiffness of the torsion tubes 554(FIGURE 2) and 556, and the stiffness of the springs 562 and 564. One ofthe principles upon which the operation of the apparatus depends is thatthe natural frequency of oscillation depends also upon the mass of theoscillating mechanical components, and this in turn depends largely uponthe specific gravity of the fluid being measured. The walls of theoscillating tube assembly are made thin so that the mass of the fluid isthe major portion of the total oscillating mass.

It will therefore be seen that the current through the amplifier tube582 (FIGURE 5) will vary at a frequency determined by the specificgravity of the fluid passing through the supply pipe.

A fluid of known specific gravity, in the embodiment shown in FIGURES 1and 2 is placed in the vibrating tube assembly 506. The conduits 596 and598 which communicate with the oscillating tube assembly 566 are thensealed. The oscillating tube assembly 566 and its associated circuitsare exactly like the oscillating tube assembly 594 and its associatedcircuits. The tube assembly 596 is oscillated by a coil 600 and appliesa signal to a pickup coil 692, the coils having armatures afiixed to thetube assembly. The coil 600 is connected in the anode circuit of avacuum tube 604 having an anode 696, a cathode 608 and a grid 610. Thepickup coil 692 is energized from a source 612 of unidirectionalpotential, through a resistor 613, and is connected in series with aresistor 614, the bottom end of which is connected to ground. A point616 at the top end of the resistor 614 is connected via condenser 618 tothe grid 610, which is biased to ground by a resistor 620. The voltageat the anode 606 will vary at a constant frequency. determined by theknown specific gravity of the reference fluid in the tube 506. It willbe understood that amplifying means other than a vacuum tube can beused, such as transistors and magnetic amplifiers.

There is provided in FIGURE 5, a network, including a resistor 622 and aresistor 624 connected in series between the anode 586 and the anode606. The resistors 622 and 624 are of the same value. The midpoint 626of these resistors will have a varying signal whose frequency is equalto the sum or difference of the signals at the anodes 586 and 606.

This varying signal from the point 626 is applied via a couplingcondenser 628 across a resistor 630, and appears at a point 632, at thetop of this resistor. From this point the signal is applied to arectifier 634, oriented in such a direction as to allow electrons topass only from left to right. The righthand electrode of this rectifieris coupled to ground via condenser 536. A point 638 connected to theupper plate of this condenser is connected to a filter comprising thecondenser 636, series resistors 640 and 642 and shunt condensers 644 and646. In parallel with the condenser 646 is a resistor 648, which inconjunction with the resistors 649 and 642 comprises the ground returnfor the rectifier-634 and the point 638. The frequency components of thevoltage at the point 659 would, except for the filter, include not onlythe frequencies at which the tubes 504 and 566 oscillate, but also theirsum and difference frequencies. The filter is of such circuit constantsas to reject the relatively high frequencies of oscillation of the tubes504 and their sum frequency, but to pass the difference frequency. Theupper end of the resistor 648 is identified as point 650.

It will be recalled that the voltage at the point 650 varies at afrequency equal to the difference in the frequencies of oscillation ofthe oscillating tubes 504 and 506. This voltage at the point 650 is moreor less sinusoidal in nature, and it can be used to operate a gage,meter, compensator, or any other means which it is desirable to haveresponsive to specific gravity.

Another arrangement for driving the oscillating tube assembly isillustrated in FIGURES 3 and 4. As shown in FIGURE 4 there is provided avacuum tube 750 which serves somewhat the same function as the tube 582of FIG. 5. A coil 752 is connected in the anode circuit of the vacuumtube, and when there is a large current through the vacuum tube, thecoil 752 attracts an-armature 754 carried by the measuring tube 756. Themeasuring tube 756, together with its inlet and discharge torsion tubesfor providing a restoring force, is of the same construction as thepreviously described measuring tubes of FIGURES 1 and 2, such as 552,the only difference being in the driving arrangement. Restoring springssimilar to 562 and 564 may be used, in addition to the restoring meansprovided by the torsion tubes, but are not shown in FIGURE 3, forsimplicity.

The control grid 758 of the vacuum tube 750 is normally biased via aresistor 766 to a negative potential derived from a terminal 762,sufficiently negative to prevent conduction through the tube 756, or toreduce the current to a value so small that the coil 752 is unable toovercome the restoring force provided by the torsion tubes and springs.The control grid is also connected with a Contact 764, which ispositioned to be engaged and disengaged by a contact 766 carried by thetube 756 as it oscillates. The contact 766 is grounded through the tube756 and its frame. The contact 764, as shown in FIGURE 3, is adapted toyield somewhat when the advancing contact 766 engages it and continuesto advance for a short distance. For this purpose, the contact 764 is ofspring construction and also its lefthand end as shown in FIGURE 3 maylift up somewhat and pivot about its righthand end when the apparatus isin a quiescent condition, that is, when the coil 752 is not energized,the spring force of the torsion tubes and the springs serves to positionthe assembly so that the contact 766 is in engagement with the contact764.

The operation of the apparatus, as may best be understood from FIGURE 4,is that, when the circuit is energized, since the grid is connected toground or cathode potential via the contacts 764 and 766, the vacuumtube 7 50 conducts strongly, and the resulting current through coil 752attracts the armature 754 and thereby moves the measuring tube 756 farenough to cause the contact 766 to disengage the contact 764. When thishappens, the potential of the grid drops to its negative bias potential,reducing the current through the coil, and allowing the measuring tubeto be restored by the spring force to its original position, and thecycle is thus repeated, causing the measuring tube to oscillate at afrequency determined by the density of the fluid in it. The outputsignal may be derived from the anode of the vacuum tube 750 and used asdescribed in connection with tubes 532 and 604 of FIG. 5. The drivingarrangement of FIGURES 3 and 4 may be used for both measuring tubes of adouble tube arrangement like that shown in FIGURE 5. It will beunderstood that the tube assemblies of FIGURES 3 and 4 arecounterbalanced for static and in some cases dynamic balance about theiraxis of oscillation, by means of counterweights.

FIGURE 6 shows still another arrangement for measuring specific gravity.This apparatus makes use of a measuring tube assembly like that shown inFIGURES l and 2, for example, tube assembly 564. An end view of such atube is shown in FIGURE 6, the tube being represented by the numeral856. In FIGURE 6 the tube 856 is driven in a manner quite different fromthe manner in which the tube assemblies are driven in FIGURE 1. It willbe understood that the tube 856 is, however, supported by torsion tubesin exactly the same manner as was the tube assembly of FIGURE 5. InFIGURE 6, there is applied to one end of the tube 856 a force adapted togive it an orbital motion. For this purpose, there are provided threecoils, 858, 862 and S64, oriented degrees apart physically, these coilsbeing connected together in a star or delta arrangement, the latterbeing shown in FIGURE 6. A three-phase current is supplied to thesecoils through the leads 866, from a source 867.

The tube 856 may be assumed to be of ferromagnetic material, adapted tobe influenced by the magnetic field supplied by the three coils 858, 862and 864. The tube may have a tough outer plastic coating. Surroundingthe tube 856 is a cylinder 868, for example, of plastic, which does notshield the tube 856 from the magnetic field of the coils. The coils aremounted symmetrically with respect to the cylinder 868, but the tube 856is in a slightly elf-center position. The rotating magnetic field willtranslate the end of the tube 856 around an orbital path, that is, willgive angular movement to the end of the tube, causing the tube to pivotabout its midpoint.

The resulting centrifugal force effect will, as the angular speedincreases, tend to cause the end of the tube to be displaced outwardlyfrom the axis of the cylinder 868. The outward displacement mentionedwill continue until the tube 856 engages the cylinder 868, whichproduces a braking effect, limiting the speed. The ultimate angularspeed will be larger when the tube 856 is filled with a light fluid,than when it is filled with a heavy fluid. This is because a heavy fluidwill, at a slower speed, produce a great enough centrifugal force toovercome the restoring force of the spring means provided by the torsiontubes, while a lighter fluid will require a greater speed to do so.

To derive an output signal, a permanent magnet is attached to theopposite end of the tube 856, and a pickup coil arranged in a positionto receive the varying flux from the magnet as it is moved about anorbital path. The output signal will have a frequency determined by thedensity of the fluid, and may be used in the same way as has beendescribed heretofore in connection with similar signals, to produce anindication of density.

The apparatus of FTGURE 6 may be of the dual type, in which oneapparatus includes a fluid to be tested and one an unknown fluid. Theresulting output signals will be compared in frequency as shown inFIGURE 5.

FIGURES 7-10 shOW another modification of the invention for determiningthe density or specific gravity of a fluid. The fluid to be tested issupplied through an inlet fitting 880 and conduit 882 to the mid portionof an inner tube 884. Fluid discharges from both ends of this inner tube884 and into sample tubes 886. The fluid flow from the ends of the innertube 884, back along the outside of this inner tube and into the openends of another and shorter inner tube 888 from which the fluid flowsthrough a conduit 890 to an outlet fitting 892. Both of the inner tubes884 and 838 are secured to a center hub 894, and these inner tubes S84and 833 have their mid portions shaped to fit into a circular openingthrough a hub 894, as shown in FIGURE 9. The conduits 882 and 890 haveflexible connections with both the hub 894 and the inlet and outletfittings 880 and 892. In the illustrated construction, these flexibleconnections are universal joints formed by having enlarged-diameterportions of the conduits contact with sealing rings S96 surrounding theend portions of the conduits which extend into both the center hub 894and the inlet and outlet fittings 889 and 892, respectively. The othermodifications of the invention can have similar universal or fiexiblejoints for connecting the oscillating tube assemblies with relativelystationary fluid passages.

The center hub 894 includes two shells 991 and 992 that clamp lips ofopposite end portions of the sample tubes to the center hub 894. Theseshells 90:. and 902 are clamped together and constitute, with the innertubes 884 and 888, and the sample tubes 886, a unitary assembly forholding the fluid to be tested. Since the fluid flows constantly throughthis assembly, the test for specific gravity is al- Ways made on thefluid flowing at the time of the determination.

There are lugs 906 and 907 extending from the shells 981 and 902,respectively, at angularly-spaced locations around the shells. Theentire sample tube assembly is supported by these lugs 906 and 907 whichhave studs 919 projecting from opposite sides of the flanges.

These extensions of the studs 910 project into helical springs 912 whichare, in turn supported from screws 914 having reduced end portions whichproject into the spring 912. The screws 914 thread through openings is afixed frame 920. These screws 914, can be rotated one way or the otherto change the compressive force on the springs 912.

Opposite sides of the frame 920 are connected together by screws 922threaded into a mid portion 924 of the frame. An outer housing 926 fitsover the frame 920 on both sides of the mid portion 924.

There is an armature 930 connected to each of the downwardly-extendinglugs 907. One of the armatures 930 is located in front of a core 932surrounded by a magnetizing coil 934. The other armature 930 is locatedin front of a core 935 surrounded by a coil 936. The cores 932 and 935,and coils 934 and 936 are integrally connected to the fixed frame 920.Energizing of the coils 934 and 936 causes the armature 936 to beattracted to these cores.

The upwardly-extending lugs 967 project through coils 938 (FIGURE 7) andthese coils are also attached to the stationary frame 920.

Energizing of the coil 934 only, with a pulsating current causes thesample tube assembly to oscillate in a plane with the direction of pullof that coil. Energizing of the coil 936 only, oscillates the sampletube assembly cause an orbital movement of the sample tubes. The naturalresonance of the sample tube assembly depends upon the spring rate ofthe spring 912 and the mass of the assembly, and it is, therefore,responsive to changes in the specific gravity of the fluid in the sampletube assembly.

The lugs 907 in unison with the rest of the assembly and their movementeffects the magnetic fields of the coils 938 and produces signalimpulses in the circuits of the coils 938.

FIGURE 11 shows the apparatus for oscillating the sample tube assembly.The assembly is designated generally by the reference character 950. Thecoil 934 is connected across opposite sides B+ and B- of a power line952 through a tube 956. The coil 936 is connected across the power line952 through a tube 954.

The coil 938 is connected across the power line 952 in series with aresistor 960. The grid of the tube 956 is connected, by a couplingcondenser 962, with a point 964 of the circuit of the coil 933 betweenthat coil and the resistor 960. The coil 938 is always energized.Another resistor 965, for biasing the grid of tube 956, is connected tothe negative side of the power line.

Current flows through the coil 934 and the tube 956 which is initiallyconducting. There is another circuit in parallel with the tube 956 andwhich includes condensers 974 and 975, a phase shifter 977 and aresistor 969. The grid of the tube 954 is connected with this parallelcircuit. When the tube 956 is conducting, the bias on the grid of thetube makes that tube nonconducting and thus the coil 936 is notenergized.

As soon as the coil 934 attracts the sample tube assembly and causes itto move, the lug 997 moves as a unit with the sample tube assembly. Thisdisturbs the field of the coil 938 and changes the voltage of thecircuit of the coils 938 and 960 with resulting change in the bias ofthe grid of the tube 956. This change in grid bias cuts off the flow ofcurrent through the tube 956 and de-energizes the coil 934.

The voltage change in the circuit of the coil 934 changes the bias onthe grid of the tube 954 so that the tube becomes conducting. Thisenergizes the coil 936 which attracts the sample tube assembly toproduce the orbital movement. The change in movement of the lug 907causes the grid of the tube 956 to again have its original bias; thetube 956 again becomes conducting; and the cycle is repeated.

This time required for the oscillations of the sample tube assemblydepends upon its mass, and is, therefore, proportional to the specificgravity of the fluid in the sample tube assembly. The frequency of theoscillations are used with suitable detection equipment to indicatespecific gravity. A specific gravity indicator 980 is showndiagrammatically connected with one of the tube circuits. This indicator980 is merely representative of means responsive to the frequency of theoscillations for indicating specific gravity.

The mutating (orbital) motion of the FIGURE 7-10 modification permitsthe density detector to weigh compressible fluids such as mixtures ofair and water. Such compressive or elastic media will not be coupled(all parts of the fluid made to have the same motion as the sample tube)to the sample tube if the tube moves sinusoidally in one plane when thetube nutates. The fluid is acted upon by centrifugal force which isuni-directional acceleration outward in a radial direction and thendidirectional in a single plane. Therefore if the fluid remains in thetube for a period of time long enough to allow all parts of the fluid toachieve the same motion as the sample tube, the fluid can be accuratelyweighed regardless of its compression.

The preferred embodiments of the invention :have been illustrated anddescribed, but changes and modifications can be made, and some featurescan be used in different combinations without departing from theinvention as described in the claims.

What is claimed is:

1. Apparatus for measuring specific gravity, comprising a hollow memberfor receiving the material to be measured, supporting means for thehollow body and on which the hollow body is movable angularly about acenter, said hollow member together with said material therein being indynamic and static balance about said center and having an equilibriumposition, means for applying a restoring force tending to restore saidhollow member to the equilibrium position when deflected angularlytherefrom about said center, means for applying periodically a force tosaid hollow member for causing it to move angularly about said centerfrom said equilibrium position at a frequency related to the specificgravity of said material therein, and frequency-responsive means,responsive to the frequency of angular movement of said hollow member,adapted to produce a definite response indicative of the specificgravity of said material in said hollow member.

2. The apparatus described in claim 1 characterized by a pair ofelongated hollow tubular members, one for containing a reference fluidof know specific gravity and the other for containing a fluid to betested, each of said tubular members being mounted for angular movementabout a neutral equilibrium position, spring means for restoring each ofsaid tubular members to its neutral position, electro-magnetic means forangularly moving each of said tubular members at a frequency determinedby the specific gravity of the fluid therein, electro-magnetic pick-upmeans for deriving two signals, correspond ing respectively in frequencyto the frequency of angular movement of said tubular members, and meansfor comparing the frequencies of said signals.

3. The apparatus described in claim 1 characterized by the hollow memberincluding a sampling tube assembly, conduits through which fluid flowsto and from the sampling tube assembly, the means for applying forceincluding electro-magnetic means for moving the tube assembly, othermeans for controlling the excitation of the electromagnetic means, saidother means including a part connected to and movable with the samplingtube assembly for shutting off the power to the electro-magnetic meanswhen the sampling tube assembly is moved by said electro-maguetic means,and said other means including also a circuit to said electro-magneticmeans closed by return of the sampling tube assembly to its originalequilibrium position whereby the electro-magnetic means is energizedrepetitively in response to movement of the sampling tube assembly whichis in turn proportional to the mass of said assembly.

4. The apparatus described in claim 3 and in which the excitation to theelectro-magnetic means is controlled by the movement of an armaturerelated to the movement of the sampling tube assembly, and there is apick-up coil related to said armature, and said movement produ-ces anelectric current flow in the pick-up coil, and there is an amplifyingmeans to which said electric current is applied to produce theaforementioned excitation to the electro-magnets, and there is anelectro-mechanical oscillator whose frequency of oscillation isproportional to the density of the fluid contained within the samplingtube assembly and the spring rate of the sampling tube assembly supportmeans.

5. The apparatus described in claim 3 and in which the apparatus has asupport on which at least a portion of the sampling tube assembly ismovable in an orbit, and the electro-magnetic means includes two magnetslocated in positions to pull the sampling tube assembly in directions indifferent planes, and said other means supply energy to the magnets withthe supply of energy to one magnet 10 out of phase with the supply ofenergy to the other magnet, whereby said magnet impart orbital movementto the sampling tube assembly.

6. The assembly described in claim 5 and in which the circuits of bothof the magnets include switch means that have triodes with the voltageon the grids of the triodes controlled by movement of the sampling tubeassembly.

7. The apparatus described in claim 6 and in which the magnets aresupplied with energy from the same source, and there is phase shifter inthe circuit of one of the magnets so that the maximum pull of theditferent magnets on the sampling tube assembly comes at differenttimes.

8. The apparatus described in claim 1 characterized by the hollow memberincluding a sampling tube assembly, an inlet fitting, an outlet fitting,both of the fittings being at fixed locations, a conduit leading fromthe inlet fitting to one part of the sampling tube assembly, anotherconduit leading from another part of the sampling tube assembly to theoutlet fitting, and flexible joints at both ends of both conduitsconnecting the conduits with the fittings and the sampling tubeassembly.

9. The apparatus described in claim 8 and in which the sampling tubeassembly includes a hub portion with a circular opening therethrough,two tubes extending through said opening and each of which is ofsemi-circular cross section and of a size to fit substantially one halfof said opening, one of the tubes connecting with the conduit from theinlet fitting and the other of the tubes connecting with the conduitfrom the outlet fitting, and both of said tubes having at least one endopen, and a shell enclosing a chamber in which the open ends of both ofthe tubes are enclosed.

10. The assembly described in claim 9 and in which the tubes extend inopposite directions from the hub portion and both tubes are open at bothends, and there are two different shells enclosing chambers on oppositesides of the hub portion, each of the shells having a flange at one endby which it is clamped to a part of the sampling tube assembly.

11. The assembly described in claim 8 and in which there are resilientsupporting means that carry the sampling tube assembly, and there areelectro-magnetic means that exert forces in directions in differentplanes to give at least a part of the sampling tube assembly an orbitalmovement.

12. The assembly described in claim 11 and in which there are armatureportions connected with the sampling tube assembly, and there areelectro-magnets located on different sides of the sampling tube assemblyand confronting the armature portions, the electromagnets extending indirections in angular relation to one another whereby saidelectro-magnets pull the sampling tube assembly in difierent directions,and means for applying repetitive excitation to each of theelectromagnets, out of phase with the other electro-magnet, to impartorbital movement to the sampling tube assembly.

13. In apparatus for measuring the density of a material, a relativelystationary supporting structure, a hollow container for said material,means connecting the container with the supporting structure andincluding a passage through which the material is supplied to the hollowcontainer, electro-magnetic means for rotating at least a portion ofsaid hollow container with respect to the supporting structure and aboutan orbital path, so as to produce a centrifugal force related to thedensity of said material in the container, the means connecting thecontainer'with the supporting structure including also spring meansoperably connected between the supporting structure and the container inposition to oppose said centrifugal force, and the resultingdisplacement of said References Cited container, and means for measuringthe frequency of said UNITED STATES PATENTS rotation as an indication ofthe density of the material 1M5 957 12/1912 Dicks 138.411 if g 1,823,9199/1931 Smith 138-111 e apparatus described 1n claim 13 whereby said 5 2635 462 4/1953 Poole et a1 spring means responsive to displacementcomprises brak- 2974525 9/1953 Cole ing means effective when saidcentrifugal force causes said 3:248:94? 5/1966 Cole container to moveoutwardly a predetermined distance in opposition to the force of saidspring so as to limit 'P A C QUEISSER, Primary Examiner said rotation toa repetition frequency determined by 10 n the density of the materialtherein. SVHNEIDER Assistant Exammell"

